In postmenopausal women, obesity is positively related to the risk of both breast and endometrial cancer. Additionally, obesity is associated with increased estrogen production secondary to increased peripheral aromatization. In postmenopausal women, this effect is proportionately more significant because the ovaries no longer contribute to production of estrogen. Obesity also alters the further metabolism of estrogens, resulting in products that retain estrogenic potency. Consequently, the estrogen-sensitive tissues of obese women are exposed to more stimulation than those tissues in leaner women. It is possible that this increased estrogen exposure is responsible for the augmented risk of breast and endometrial cancer observed in obesity. Evidence is accumulating that dietary macronutrients can alter the metabolism and excretion of endogenous estrogen and androgen, providing a potential mechanism by which diet can modulate the risk of hormone-sensitive cancers.